A device for transporting powder is known from the publication EP 1 427 536 B1. The conveying device includes a first conveying chamber and a second conveying chamber located parallel to it, whereby each of the conveying chambers is fitted with a feed line and a discharge line for the powder to be conveyed. Both discharge lines are connected together on the discharge side. While powder is sucked in via the feed line in the first conveying chamber, the powder from a previous work cycle being in the second conveying chamber is transported away via the discharge line. The conveyed powder in the first conveying chamber is subsequently transported away from the conveying chamber, while fresh powder is sucked into the second conveying chamber from the powder reservoir. The first conveying chamber creates, together with a drive unit and a piston, a pump. The second conveying chamber creates, together with a second drive unit and a second piston a second pump. Both pumps operate out of phase with each other but synchronously. This allows reduction of pulsing in the stream of powder flowing to the spray gun. However, as explained above, two pumps are necessary which leads to an increase in the installation space required and to a rather more complex construction. Also, since a range of driven mechanical parts are needed, the wear and the susceptibility to failure of the conveying device are not insubstantial.
A powder conveying device is known from the prior art DE 103 00 280 A1, which is also declared as a pumping system for powder. This pumping system consists of two mechanically synchronized membrane pumps which transport the coating powder alternately. Each of the membrane pumps is fitted with an inlet valve, a dosing chamber and an outlet valve. If the inlet valve is opened and a vacuum is generated in the dosing chamber with the aid of a disc-shaped membrane then powder is sucked into the dosing chamber. The inlet valve is then closed and the coating powder from the dosing chamber is blown out of the dosing chamber via the now opened outlet valve with the aid of compressed air which is blown into the dosing chamber. Movement of the membranes of the two membrane pumps takes place via a piston rod which connects the two membranes together. In this way, as the chamber volume of the first dosing chamber is increased with the aid of the membrane, the chamber volume of the second dosing chamber is automatically reduced. Such a conveying device for powder is complex to manufacture. It is also a considerably effort to control the drive, that is to say the piston rod. Just detecting the position of the piston rod requires four sensors. A further disadvantage is that the conveying device takes a lot of effort to be cleaned when a color change is made.